Section 2- Cell structure Flashcards
What is resolution?
The minimum distance apart 2 objects can be in order for the to appear as separate items.
What is magnification?
How many times bigger the image is when compared to the object.
How do you convert from millimetres to micrometres?
Multiply by 1000
What of these organelles does a virus have?
- Cell-surface membrane
- Nucleus
- Cytoplasm
- Capsid
Only capsid
no cell-surface membrane, nucleus, cytoplasm
Why can mitochondria look different to one another?
Very in shape
Cut in different planes
What are 3 reasons why mitosis is important to organisms?
Asexual reproduction
Growth in organisms
Repair in organisms
What are 3 ways DNA in chloroplast is different to DNA in nucleus?
Fewer genes
Shorter in length
No introns
Circular not linear
Why are organelle structures not visible in optical microscopes?
Resolution is not high enough
Light microscope have longer wavelength
What organelle is found in both chloroplast and prokaryotic cell?
Ribosomes
What type of cell wall is found in plants, algae, fungi and prokaryotes?
(cellulose, murein, chitin)
Plants: cellulose
Algae: cellulose
Fungi: chitin
Prokaryotes: murein
What is the structure of a prokaryote?
Cell wall
Capsule: protects bacteria form other cells
Cell-surface membrane
Circular DNA
Plasmid: has genes that may aid survival of bacteria
What is the difference between prokaryotic and eukaryotic cells?
Eukaryotic cells: Distinct nucleus with envelope DNA associated with proteins No plasmids, DNA is linear Membrane bound organelles Ribosomes are larger
Prokaryotic: No nucleus Some DNA in plasmids No membrane-bound organelles Ribosomes are smaller Cell wall made of murein Have capsule
What 2 types of molecules are ribosomes made from?
Ribosomal RNA
Protein
What is the molecule found in the cell walls of bacterial cells?
Murein
Why can light microscopes only distinguish between 2 objects if they are 0.2um apart?
Due to the relatively long wavelength of light.
What are the evaluative points for a light microscope?
Low resolution
- Due to long wavelength of light
- Limits magnification
Able to view living specimen
Able to see colour (with stain)
Simple preparation
Artefacts are rare
What are the evaluative points of an electron microscope?
Uses beam of electrons to produce an image
High resolution
-Short wavelength of electrons
Sample must be dead
-Chamber is a vacuum
Image produced is black and white
Preparation is complicated
Artefacts are common
What are the 2 types of electron microscope?
Transmission electron microscope
Scanning electron microscope
What is a transmission electron microscope?
Passes beam of electrons through a very thin specimen
Parts of the specimen allow electrons to pass through and so appear bright
What are the limitations of a transmission electron microscope?
Difficult preparation limits resolution
System is a vacuum = dead specimen
Image is 2D and black and white
May contain artefacts
What is a scanning electron microscope?
Produced a 3D image of the surface of the object
Resolution isn’t as high
3D image can be built by computer analysis of the pattern and secondary electrons
What are the 2 processes of cell fractionation?
Homogenisation
Ultracentrifugation
What 3 kind of solutions does a tissue need to be placed in before cell fractionation?
Cold
Isotonic
Buffer
What does a tissue need to be placed in a cold solution before cell fractionation?
Reduces activity of enzymes which may break down organelles
Why does a tissue need to be placed in a isotonic solution before cell fractionation?
Prevent shrining and bursting due to osmosis
What does a tissue need to be placed in a buffer solution before cell fractionation?
To maintain a constant pH, avoiding damage to organelles
Why is a tissue firstly placed in a homogeniser and filtered before going in a centrifuge?
Releases organelles from the cells
Filtered to remove any whole cells and large debris (cell wall)
What is the process of cell fractionation?
- Tissue placed in cold, isotonic, buffer solution.
- Homogenisation
- Filter homogenate
- Centrifuge homogenate and collect sediment
- Spin at faster speeds and collect sediment
What is the order of organelles in the sediment of an animal cell when centrifuged?
Nuclei
Mitochondria
Lysosomes
What is the structure and function of the mitochondria?
Double membrane: controls entry and exit of material
Cristae (extensions of inner membrane): provide large surface area for enzyme attachment
Matrix: contains proteins, lipids, ribosomes, DNA that allow mitochondria to control production of proteins
What is the structure and function of the chloroplast?
Chloroplast envelope: controls entry and exit of substances
Grana: stacks of thylakoids which contain the chlorophyll
Granal membranes provide large surface area
Stroma: contain starch grains
Grana & stroma: both for photosynthesis
What is the structure and function of the chloroplast?
Chloroplast envelope: controls entry and exit of substances
Grana: stacks of thylakoids which contain the chlorophyll
Stroma: contain starch grains
Grana & stroma: both for photosynthesis
What is the structure and function of the smooth endoplasmic reticulum?
Synthesises and processes lipids
Secretes steroids
System of hollow tubes: allows transport of substances within cells
Site of carbohydrate and lipid metabolism
What is the structure and function of the rough endoplasmic reticulum?
Covered in ribosomes: synthesise proteins which are transported through cell cavities
Hollow tubes: allow transport of substances within the cell
Folds and processes proteins that have been made at the ribosomes.
Provides large surface area for synthesis of proteins and glycoproteins
What is the structure and function of the golgi apparatus?
Processes and packages new lipids and proteins
Makes lysosomes
Flattened membrane cavities: allows internal transport
Vesicles: contain material to be secreted and protect molecules
Connected to RER: proteins are modified before secretion
What is the structure and function of the lysosomes?
Vesicles which contain hydrolytic enzyme (lysozyme): break down old organelles
Used to digest invading cells or break down worn out component of the cell
What is the structure and function of the ribosome?
80s- eukaryotic cells
70s- prokaryotic cells, mitochondria, chloroplast
2 subunits both made of protein and rRNA
Provide binding site for mRNA which allow translocation of DNA code
What is the structure and function of the ribosome?
80s- eukaryotic cells
70s- prokaryotic cells, mitochondria, chloroplast
2 subunits both made of protein and rRNA
Provide binding site for mRNA which allow translocation of DNA code
What is the structure and function of the cell wall?
Consists of microfibrils of cellulose embedded in a matrix
Provide strength and rigidity
What is the structure and function of the vaculole?
Single membrane = tonoplast
Fluid filled sac of cell-sap (sugar & salts)
Helps to maintain pressure inside - stop plant wilting
Why is the electron microscope able to resolve objects better than the light microscope?
The electron microscope uses a beam of electrons that has a much smaller wavelength than light
Why do specimens have to be kept in a near-vacuum in order to be viewed effectively using an electron microscope?
Electrons are absorbed by molecules in the air which would prevent the electrons reaching the specimen
Why can the theoretical resolving power of an electron microscope not always be achieved?
Preparation of specimens may not be good enough
Higher energy electron beam is required and this may destroy the specimen
Why can the theoretical resolving power of an electron microscope not always be achieved?
Preparation of specimens may not be good enough
Higher energy electron beam is required and this may destroy the specimen
What is cell differentiation?
When a cell develops specific structures and becomes specialised to carry out a particular function
What are some common cell adaptations?
Folded membrane / microvilli = increase surface area
Increases mitochondria = large amounts of ATP for active transport
Walls one cell thick to reduce diffusion distance
What is the role of plasmids in prokaryotes?
Small ring of DNA that carries non-essential genes
What is the role of the flagella in prokaryotes?
Rotating tail propels organism
What is the role of the capsule in prokaryotes?
Protects bacterium from other cells and help groups of bacteria to stick together for further protection
What is the role of the circular DNA in prokaryotes?
Contains genetic material
What is the basic structure of a virus?
Capsid: protects genetic information
Envelope
Attachment proteins
Genetic information
What are the 5 stages of a viruses life cycle?
Attachment Entry Replication Assembly Release
What are the 3 phases of the cell cyle?
Interphase: cell growth and DNA replication
G1= cell growth
S phase= DNA synthesises
G2= proteins synthesised
Nuclear division: mitosis/ meiosis
Cytokinesis: division of cytoplasm
What is mitosis for?
Growth
Repair
Replacement
Asexual reproduction
What is an advantage and disadvantage of mitosis?
Genetic make-up of parent has enabled survival and reproduction
Genetic variation is limited
What are the 4 phases of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase of mitosis?
Chromosomes condense getting shorter and fatter
Nuclear envelope breaks down, chromosomes lie free
Centrioles start moving opposite ends, forming spindle
What happens during metaphase of mitosis?
Chromosomes line up along equator
Chromosomes become attached to spindle by centromere
What happens during anaphase of mitosis?
Centromere divides, separating into chromatids
Spindles contract, pulling chromatids to each pole
What happens during telophase of mitosis?
Chromatids reach opposite poles on the spindle
Chromatids uncoil, becoming long & thin
Nuclear envelope forms
How does cell division in prokaryotes occur?
Binary fission
- Circular DNA molecule replicated, both copies attach to cell membrane
- Cell membrane begins to grow between 2 DNA molecules, begins to pinch inwards
- New cell wall forms between 2 molecules of DNA, divides original cell into 2 identical daughter cells
What are malignant tumours?
Grow rapidly
Less compact
Invade surrounding tissues
More likely to be life-threatening
What is cancer caused by?
Mutation in gene causes uncontrolled mitosis
Mutations can form clones of themselves, forming tumours
How do drugs normally treat cancer?
Prevent DNA replicating
Inhibit metaphase by interfering with spindle formation
Why do ciliated cells contain relatively large numbers of mitochondria?
ATP produced is needed for the movement/ wafting of cilia.
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells.
Nucleotide structure is identical
Nucleotides joined by phosphodiester bond
Eukaryotic DNA is longer, contains introns
Eukaryotic DNA is linear, prokaryotic is circular
Eukaryotic DNA is associated with histones, prokaryotic is not.
What would be a method of testing for starch?
Thin slice sample
Stain with iodine
Why would a student use a homogeniser?
To break open cells
Why would a solution be buffered?
No change in pH
To prevent denaturation of proteins
Why would students use a stain that turns DNA blue when observing mitosis?
Make chromosome visible
Chromosome contains DNA
What would be a method of displaying results in a pie chart?
Draw circle
(Number of section/ Total number) X 360
Use protractor
What is the stage of the cell cycle during which chromosomes replicate?
S phase in Interphase
What is a process that occurs during G1 and G2 of the cell cycle?
Growth of cell
How common is a flagellum in eukaryotic and prokaryotic cells?
Sometimes present in both
How could you improve a biological drawing?
No shading No overlapping lines Scale Title Labels of key features
When a fish is removed from water, their lamellae stick together.
How can this be damaging to fish?
Lamellae stick together, surface area is reduced so not enough oxygen is absorbed
A different set of results were obtained when count was repeated in mitotic index with a different garlic root tip. Give two reasons for the difference in results.
Genetic difference, time, chance, age of root tip
What are 2 reasons why it is important to the count number of organelles in several parts of a tissue?
To obtain a reliable mean
Distribution may not be uniform
What happens within a vacuole after it fuses with the lysosome?
Enzymes used in hydrolysis
Digestion of bond
Why would an image of low magnification be of little use when studying cells?
Low resolution as wavelength of light is too long
Why do ciliated cells contain large numbers of mitochondria?
ATP is needed for movement of cilia
